我需要一些帮助,在scala中的这段代码,我想实现foldL方法,但得到的是这样的结果。
asd.scala:73: error: type mismatch;
found : Option[MyTree[A]] => B
required: B
def myFoldLeft[B](z: B)(op: (B, A) => B): B = (_:Option[MyTree[A]]) match {
^
one error found
我知道这是一个类型错误匹配,但我是Scala和面向对象的新手,我不明白如何解决这种情况。
class MyTree[A](val value: A, val left:Option[MyTree[A]],
val right:Option[MyTree[A]]) {
def myFoldLeft[B](z: B)(op: (B, A) => B): B = (_:Option[MyTree[A]]) match {
case Some(tree) => right.get.myFoldLeft (left.get.myFoldLeft (op(z, value)) (op)) (op)
case None => z
}
}
(_:Option[MyTree[A]]) ...
是一个lambda。
你应该像这样匹配
class MyTree[A](val value: A, val left:Option[MyTree[A]],
val right:Option[MyTree[A]]) {
def myFoldLeft[B](z: B)(op: (B, A) => B): B = (left, right) match {
case (Some(left), Some(right)) => ???
case (Some(left), None) => ???
case (None, Some(right)) => ???
case (None, None) => ???
}
}